Sheet feeding device and image forming apparatus

ABSTRACT

A sheet feeding device includes a feeding member that rotates and feeds a sheet; a resistance member that contacts the feeding member with the sheet interposed therebetween, the resistance member contacting the sheet fed by the feeding member and applying a resistance against the feeding of the sheet; a holding unit that holds the resistance member so that the resistance member is movable to a position where the resistance member does not contact the feeding member; and an urging unit that urges the resistance member held by the holding unit in a direction opposite to a feeding direction of the sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2013-085113 filed Apr. 15, 2013.

BACKGROUND Technical Field

The present invention relates to a sheet feeding device and an image forming apparatus.

SUMMARY

According to an aspect of the invention, there is provided a sheet feeding device including a feeding member that rotates and feeds a sheet; a resistance member that contacts the feeding member with the sheet interposed therebetween, the resistance member contacting the sheet fed by the feeding member and applying a resistance against the feeding of the sheet; a holding unit that holds the resistance member so that the resistance member is movable to a position where the resistance member does not contact the feeding member; and an urging unit that urges the resistance member held by the holding unit in a direction opposite to a feeding direction of the sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 illustrates the structure of an image forming apparatus according to an exemplary embodiment of the present invention;

FIG. 2 is a side view of a feeding device according to the exemplary embodiment of the present invention;

FIG. 3 is a perspective view of a part of the feeding device illustrated in FIG. 1;

FIG. 4 is a perspective view of a resistance roller included in the feeding device illustrated in FIG. 1;

FIG. 5 is a side view of the feeding device illustrated in FIG. 1 in a state immediately after the start of a recording medium feeding process;

FIG. 6 is a side view of the feeding device in a state in which the recording medium has been transported from the state illustrated in FIG. 5;

FIG. 7 is a schematic side view of a feeding device according to a first modification;

FIG. 8A is a schematic side view of a feeding device according to a second modification;

FIG. 8B is a side view of the feeding device in a state in which a recording medium is being fed; and

FIG. 9 is a diagram illustrating the relationship between a force that tries to rotate a resistance roller and a force that is applied to the resistance roller by a recording medium in a feeding direction S.

DETAILED DESCRIPTION

An image forming apparatus according to an exemplary embodiment of the present invention will now be described.

Overall Structure

First, the structure of an image forming apparatus 10 according to the present exemplary embodiment will be described. FIG. 1 schematically illustrates the structure of the image forming apparatus 10 according to the present exemplary embodiment. The arrow UP in FIG. 1 indicates the upward vertical direction.

The image forming apparatus 10 according to the present exemplary embodiment illustrated in FIG. 1 includes an image forming apparatus body 11 that houses components therein. The image forming apparatus body 11 houses a container 12 in which sheet-shaped recording media P, such as sheets of recording paper and OHP sheets, are stored; an image forming section 14 that forms an image on a recording medium P; a feeding device 100 that feeds a sheet-shaped recording medium P from the container 12; a transport unit 16 that transports the recording medium P that has been fed to the image forming section 14; and a controller 20 that controls the operation of each component of the image forming apparatus 10. An ejection unit 18, to which the recording medium P having an image formed thereon by the image forming section 14 is ejected, is provided in an upper section of the image forming apparatus body 11.

The image forming section 14 includes image forming units 22Y, 22M, 22C, and 22K (hereinafter denoted by 22Y to 22K) that form toner images of respective colors, which are yellow (Y), magenta (M), cyan (C), and black (K), respectively; an intermediate transfer belt 24 onto which the toner images formed by the image forming units 22Y to 22K are transferred; first transfer rollers 26 that transfer the toner images formed by the image forming units 22Y to 22K onto the intermediate transfer belt 24; and a second transfer roller 28 that transfers the toner images, which have been transferred onto the intermediate transfer belt 24 by the first transfer rollers 26, onto the recording medium P from the intermediate transfer belt 24. The structure of the image forming section 14 is not limited to the above-described structure as long as an image may be formed on the recording medium P.

The image forming units 22Y to 22K are arranged next to each other in a central region of the image forming apparatus body 11 in the vertical direction while being tilted with respect to the horizontal direction. Each of the image forming units 22Y to 22K includes a photoconductor 32 that rotates in a certain direction (for example, clockwise in FIG. 1). Since the image forming units 22Y to 22K have similar structures, components of the image forming units 22M, 22C, and 22K are not denoted by reference numerals in FIG. 1.

A charging roller 23, an exposure device 36, a developing device 38, and a removing member 40 are arranged around each photoconductor 32 in that order from an upstream side in a rotation direction of the photoconductor 32. The charging roller 23 is an example of a charging device that charges the photoconductor 32. The exposure device 36 performs an exposure process on the photoconductor 32 charged by the charging roller 23 to form an electrostatic latent image on the photoconductor 32. The developing device 38 develops the electrostatic latent image formed on the photoconductor 32 by the exposure device 36 to form a toner image. The removing member 40 contacts the photoconductor 32 and removes toner that remains on the photoconductor 32.

The exposure device 36 forms the electrostatic latent image on the basis of an image signal transmitted from the controller 20. The image signal transmitted from the controller 20 may be, for example, an image signal transmitted to the controller 20 from an external device.

The developing device 38 includes a developer supplying unit 38A that supplies developer to the photoconductor 32 and plural transport members 38B that transport the developer to be supplied to the developer supplying unit 38A while stirring the developer.

The intermediate transfer belt 24 has an annular shape and is located above the image forming units 22Y to 22K. Stretching rollers 42 and 44, around which the intermediate transfer belt 24 is wrapped, are disposed inside the intermediate transfer belt 24. When one of the stretching rollers 42 and 44 is rotated, the intermediate transfer belt 24 moves (rotates) in a certain direction (for example, counterclockwise in FIG. 1) while being in contact with the photoconductors 32. The stretching roller 42 serves as an opposing roller that opposes the second transfer roller 28.

The first transfer rollers 26 oppose the respective photoconductors 32 with the intermediate transfer belt 24 interposed therebetween. The positions between the first transfer rollers 26 and the photoconductors 32 serve as first transfer positions at which the toner images formed on the photoconductors 32 are transferred onto the intermediate transfer belt 24.

The second transfer roller 28 opposes the stretching roller 42 with the intermediate transfer belt 24 interposed therebetween. The position between the second transfer roller 28 and the stretching roller 42 serves as a second transfer position at which the toner images that have been transferred onto the intermediate transfer belt 24 are transferred onto the recording medium P.

The feeding device 100 is configured to separate the sheet-shaped recording media P stored in the container 12 from each other and feed them one by one to the transport unit 16 to avoid simultaneous feeding of two or more recording media P to the transport unit 16. The feeding device 100 will be described in detail below.

The transport unit 16 includes a transport path 48 along which each recording medium P is transported and plural transport rollers 50 that are arranged along the transport path 48 to transport the recording medium P to the second transfer position.

The image forming apparatus body 11 houses a fixing device 60 at a location downstream of the second transfer position in a transport direction. The fixing device 60 fixes the toner images that have been transferred onto the recording medium P by the second transfer roller 28 to the recording medium P. The fixing device 60 may be attached to and detached from the image forming apparatus body 11 in a manufacturing process, but is not detachable by a user. The fixing device 60 includes ejection rollers 52 that eject the recording medium P having the toner images fixed thereto to the ejection unit 18.

The fixing device 60 includes a heating roller 64 and a pressing belt 66 as examples of fixing members for fixing the toner images to the recording medium P.

The heating roller 64 includes a cylindrical member 64A that is rotatably supported in the fixing device 60 and a heat source 64B, such as a halogen lamp, disposed in the inner space of the cylindrical member 64A. The pressing belt 66 has an annular shape and is rotatably supported in the fixing device 60 at a position where the pressing belt 66 opposes the heating roller 64.

The heating roller 64 and the pressing belt 66 rotate around a rotation axis direction, which is a width direction of the recording medium P (hereinafter referred to simply as a width direction) that is orthogonal to a transport direction of the recording medium P (hereinafter referred to simply as a transport direction), and extend in the width direction.

When the heating roller 64 is rotated and the pressing belt 66 is rotated by the rotation of the heating roller 64, the recording medium P onto which the toner images have been transferred is transported while being nipped between the heating roller 64 and the pressing belt 66. The toner on the recording medium P that is transported while being nipped between the heating roller 64 and the pressing belt 66 is heated by the heating roller 64 and pressed by the pressing belt 66, so that the images are fixed to the recording medium P.

The fixing device 60 is equipped with a pair of ejection rollers 52 for ejecting the recording medium P having the toner images fixed thereon by the heating roller 64 and the pressing belt 66 to the ejection unit 18 from the fixing device 60. The pair of ejection rollers 52 include a driven roller 52A and a drive roller 52B disposed below the driven roller 52A.

The image forming apparatus body 11 includes a reverse transport path 70 for returning the recording medium P having images formed on one side thereof to the transfer position (image forming position) with plural transport rollers 50 to allow images to be formed on both sides of the recording medium P.

The fixing device 60 includes an introduction path 49 that guides the recording medium P having images fixed thereto to the reverse transport path 70. The introduction path 49 is configured to guide the recording medium P having images fixed thereto that has been transported backward by reverse rotation of the ejection rollers 52 to the reverse transport path 70. Thus, in the image forming apparatus 10, the recording medium P having the images formed on one side thereof may be reversed and returned to the transport path 48 by the introduction path 49 and the reverse transport path 70.

Image Forming Operation

Next, an image forming operation performed by the image forming apparatus 10 according to the present exemplary embodiment to form an image on the recording medium P will be described.

In the image forming apparatus 10 according to the present exemplary embodiment, a recording medium P is fed from the container 12 by the feeding device 100, and is transported to the second transfer position by the transport rollers 50.

In each of the image forming units 22Y to 22K, the photoconductor 32 is charged by the charging roller 23 and subjected to the exposure process by the exposure device 36, so that an electrostatic latent image is formed on the photoconductor 32. The electrostatic latent image is developed by the developing device 38, so that a toner image is formed on the photoconductor 32. The toner images of the respective colors formed by the image forming units 22Y to 22K are transferred onto the intermediate transfer belt 24 in a superimposed manner at the first transfer positions, so that a color image is formed. The color image formed on the intermediate transfer belt 24 is transferred onto the recording medium P at the second transfer position.

The recording medium P onto which the toner images have been transferred is transported to the fixing device 60, and the toner images are fixed to the recording medium P by the fixing device 60. In the case where an image is to be formed only on one side of the recording medium P, the recording medium P is ejected to the ejection unit 18 by the ejection rollers 52 after the toner images are fixed.

In the case where images are to be formed on both sides of the recording medium P, the recording medium P having an image formed on one side thereof is transported from the introduction path 49 to the reverse transport path 70 by the reverse rotation of the ejection rollers 52. Then, the recording medium P is transported from the reverse transport path 70 to the transport path 48, and an image is formed on the other side of the recording medium P by a process similar to the above-described process. Thus, images are formed on both sides of the recording medium P. Thus, the image forming operation is performed.

Feeding Device

The feeding device 100 will now be described. FIG. 2 is a side view illustrating the state before or after the recording medium P is fed, and FIGS. 5 and 6 are side views illustrating the state in which the recording medium P is being fed.

As illustrated in FIG. 2, the feeding device 100 includes a feeding roller 110 disposed at an upper location and a resistance roller 120 disposed at a lower location so as to oppose the feeding roller 110. The direction of rotation axes of these rollers may sometimes be referred to as a width direction. As illustrated in FIG. 5, for example, the direction in which the recording medium P is fed by the feeding roller 110 is defined as a feeding direction S.

The feeding roller 110 is substantially D-shaped (half moon shaped) and the outer periphery thereof is chamfered (D-cut) to form a substantially flat portion. The substantially flat portion is called a D-cut portion 114. A feeding member 112, which is made of rubber or the like, is provided on the outer periphery of the feeding roller 110 in a region other than the D-cut portion 114. The feeding roller 110 is rotatable in the direction of arrow K1 by a driving mechanism (not shown).

Rotating plates (not shown) are provided on both sides of the feeding roller 110. The rotating plates have a diameter smaller than that of the feeding roller 110, and are configured to prevent the feeding member 112 and the resistance roller 120 from contacting each other in the state before and after the recording medium P is fed. The rotating plates (not shown) are formed by molding a resin, such as POM.

As illustrated in FIGS. 2 and 3, the resistance roller 120 is rotatably supported by the holder member 150. Shaft portions 152 are provided on both sides of the holder member 150 in the width direction at a downstream position in the feeding direction S. The holder member 150 is rotatably supported on a housing (not shown) or the like by the shaft portions 152.

As illustrated in FIG. 2, a coil spring 154 is disposed below the holder member 150. The bottom end of the coil spring 154 is fixed to the housing (not shown) or the like. The holder member 150 is urged by an urging force of the coil spring 154 so as to rotate around the shaft portions 152. Thus, the resistance roller 120 held by the holder member 150 is urged toward the feeding roller 110. A stopper (not shown) is provided so that the rotation of the holder member 150 is stopped at a predetermined position.

Referring to FIG. 5, when the feeding roller 110 is rotated in the direction of arrow K1, a contact pressure is applied to a contact portion (hereinafter referred to as a nip N) between the feeding member 112 of the feeding roller 110 and a resistance member 130 of the resistance roller 120 by the urging force of the coil spring 154.

The shaft portions 152 of the holder member 150 are configured such that the urging force applied to the resistance roller 120 held by the holder member 150 is greater when the resistance member 130 is in contact with the feeding member 112 of the feeding roller 110 than when the resistance member 130 is not yet in contact with the feeding member 112 of the feeding roller 110. In other words, the shaft portions 152 of the holder member 150 are positioned so that the contact force applied between the feeding member 112 and the resistance member 130 increases when the resistance member 130 applies a resistance to the recording medium P.

As illustrated in FIGS. 2 to 4, the resistance roller 120 includes a roller body 122 that is rotatably held by the holder member 150 (see FIGS. 2 and 3) and the resistance member 130 made of rubber that is provided over a part of the outer periphery of the roller body 122 so as to oppose the feeding roller 110. The resistance member 130 has an arc shape in side view.

A projection 126 and a rotation shaft 124 that is rotatably supported by the holder member 150 (see FIGS. 2 and 3) are provided on each end of the resistance roller 120 (roller body 122) in the width direction. The resistance roller 120 is held by the holder member 150 so as to be rotatable in the direction of arrow K2 and the direction of arrow K3.

The rotational range (movable range) of the resistance member 130 of the resistance roller 120 toward the upstream side in the feeding direction (in the direction of arrow K3) is set so that an end 132 of the resistance member 130 in the feeding direction does not move past the nip N (see FIG. 5) between the resistance roller 120 and the feeding roller 110. In other words, the rotation of the resistance roller 120 in the direction of arrow K3 is stopped by a stopper (not shown) at the position shown in FIG. 2. The feeding roller 110 and the resistance roller 120 do not become separated from each other even when the resistance roller 120 is rotated in the direction of arrow K3.

The rotational range (movable range) of the resistance member 130 of the resistance roller 120 toward the downstream side in the feeding direction (in the direction of arrow K2) is set so that an end 134 of the resistance member 130 opposite to the end in the feeding direction moves past the nip N (see FIG. 5) between the resistance roller 120 and the feeding roller 110 (see FIG. 6). In other words, the resistance roller 120 is held by the holder member 150 so that the resistance roller 120 rotates in the direction of arrow K2 until the upstream end 134 of the resistance member 130 of the resistance roller 120 in the feeding direction (end in the direction of arrow K3) moves past the nip N (see FIG. 5) between the resistance roller 120 and the feeding roller 110 (see FIG. 6).

As illustrated in FIGS. 2 and 3, a torsion coil spring is fitted to the rotation shaft 124 of the resistance roller 120 (roller body 122). One end portion 142 of the torsion coil spring 140 is wound around the projection 126, and the other end portion 146 of the torsion coil spring 140 is retained by a retaining portion 156 of the holder member 150. Thus, the resistance roller 120 is urged so as to rotate in the direction of arrow K3, that is, in a direction opposite to the feeding direction S. The resistance roller 120 receives a torque in the direction of arrow K3 (direction opposite to the feeding direction S) from the torsion coil spring 140.

Although only one side in the width direction (axial direction) is illustrated in FIGS. 2 and 3, the structure at the other side is similar to that at the illustrated side, and the rotation shaft 124, the projection 126, the torsion coil spring 140, and the retaining portion 156 are provided. More specifically, the torsion coil spring 140 is provided at each end of the resistance roller 120 (resistance member 130) in the width direction (axial direction).

Operation

The operation of the present exemplary embodiment will now be described.

As illustrated in FIG. 5, the topmost one of the recording media P in a stacked state is fed when the substantially D-shaped (half moon shaped) feeding roller 110 is rotated.

As described above, a nip pressure is applied to the nip N between the feeding member 112 of the feeding roller 110 and the resistance member 130 of the resistance roller 120 by the urging force of the coil spring 154. In addition, the resistance roller 120 (the resistance member 130) receives a torque in the direction of arrow K3 (direction opposite to the feeding direction) owing to the urging force of the torsion coil spring 140.

When a single recording medium P is fed by the feeding roller 110, the resistance roller 120 (resistance member 130) receives a rotational force in the direction of arrow K2 through the recording medium P, and rotates in the direction of arrow K2 (feeding direction) against the urging force of the torsion coil spring 140.

Referring to FIG. 9, when Np is the nip pressure applied by the resistance member 130 of the resistance roller 120 that presses the feeding member 112 of the feeding roller 110, μ is the coefficient of friction of the resistance member 130 of the resistance roller 120, r is the radius of the resistance roller 120, and T is the torque of the torsion coil spring 140, a force Fr that tries to rotate the resistance roller 120 in the direction of arrow K3 is calculated as Fr=T/r.

A force Fp applied to the resistance roller 120 (resistance member 130) by the recording medium P in the feeding direction S is calculated as Fp=Np×μ.

In order for the recording medium P to be transported, that is, in order for the resistance roller 120 to be rotated in the direction of arrow K2, Fp>Fr needs to be satisfied.

The image forming apparatus 10 is designed so that Fp>Fr is satisfied as long as the recording medium P is of a type that is capable of being subjected to a printing process performed by the image forming apparatus 10.

As illustrated in FIG. 6, when the end portion 134 of the resistance member 130 of the resistance roller 120 in the direction of arrow K3 (direction opposite to the feeding direction) moves past the nip N, the resistance roller 120 is rotated in the direction of arrow K3 by the urging force of the torsion coil spring 140, so that the end portion 134 returns to the nip N. However, the resistance roller 120 soon rotates in the direction of arrow K2 (feeding direction) again owing to the frictional force between the recording medium P and the resistance member 130, so that the end portion 134 of the resistance member 130 of the resistance roller 120 is moved past the nip N. In other words, the end portion 134 of the resistance member 130 repeatedly moves past and returns to the nip N (small motion).

In the case where plural recording media P are fed together by the feeding roller 110 (in case of double feeding), the topmost recording medium P that is in contact with the feeding member 112 of the feeding roller 110 is further transported by the feeding roller 110. Since the frictional resistance between the recording media P is small, one or more recording media P below the topmost recording medium P are stopped owing to a transport load (transport resistance) of the resistance member 130 of the resistance roller 120 that tries to rotate in the direction of arrow K3 (direction opposite to the feeding direction), and are pushed backward in the direction of arrow K3. The recording media P below the topmost recording medium P are pushed back past the nip N toward the downstream side in the feeding direction. Thus, the recording media P are separated from each other and only the topmost recording medium P is fed to the transport unit 16 (see FIG. 1). As described above, the image forming apparatus 10 is designed so that Fp>Fr is satisfied. Therefore, as long as the recording medium P is of a type that is capable of being subjected to the printing process performed by the image forming apparatus 10, the end portion 134 of the resistance member 130 of the resistance roller 120 moves past the nip N.

As described above, in the feeding device 100 according to the present exemplary embodiment, the urging force (spring force) of the torsion coil spring 140 serves as the transport load (transport resistance) applied to the recording medium P. Therefore, the transport load (transport resistance) may be defined by the urging force (spring force) of the torsion coil spring 140. Accordingly, even when the surface of the resistance member 130 has dust or the like attached thereto, the transport load (transport resistance) changes by a smaller amount than in the case where the resistance member is fixed (in the case where the transport load (transport resistance) is defined by the frictional resistance and the nip pressure). In other words, feeding failure, double feeding, etc., of the recording media P may be prevented or suppressed.

The torsion coil spring 140 is provided at each end of the resistance roller 120 (resistance member 130) in the width direction (axial direction). Therefore, compared to the case in which the torsion coil spring 140 is provided only at one end in the width direction, variation in transport load along the width direction (axial direction) is reduced (the transport load is made uniform).

The torsion coil spring may be disposed inside the resistance roller. Also in such a case, the spring (urging unit) is disposed on each side of a central region in the width direction (axial direction) to reduce variation in the transport load along the axial direction. Alternatively, the spring (urging unit) may be disposed only in the central region in the width direction (axial direction). In the case where plural resistance rollers are arranged in the axial direction, spring (urging units) may be disposed between the resistance rollers.

When the feeding process performed by the feeding roller 110 is finished, that is, when the D-cut portion 114 of the feeding roller 110 is positioned so as to face the resistance roller 120, the resistance roller 120 is rotated in the direction of arrow K3 by the urging force of the torsion coil spring 140, and returns to the original position, as illustrated in FIG. 2. As a result, the recording media P that have been separated from the topmost recording medium P and that remain at a position near the downstream end of the nip N in the feeding direction are pushed back in the direction of arrow K3. Thus, displacements of the recording media P from the predetermined position (regular position) may be suppressed.

A comparative example will now be considered in which the movable range (rotatable range) of the end portion 134 of the resistance member 130 of the resistance roller 120 is such that the end portion 134 does not move past the nip N.

When the feeding roller 110 is rotated, the recording medium P is fed and the resistance roller 120 is also rotated. When the end portion 134 of the resistance member 130 in the direction of arrow K3 stops before it moves past the nip N, the frictional force and nip pressure of the resistance member 130, instead of the urging force of the torsion coil spring 140, serve as the transport load (transport resistance). This is the same as the case where the resistance member is fixed (case where the transport load (transport resistance) is defined by the frictional resistance and nip pressure), and the urging force (spring force) of the torsion coil spring 140 does not serve as the transport load (transport resistance) applied to the recording medium P.

In the present exemplary embodiment, as described above, the rotational range of the resistance member 130 of the resistance roller 120 toward upstream side in the feeding direction (in the direction of arrow K2) is set such that the end portion 134 at the end opposite to the end in the feeding direction moves past the nip N (see FIG. 2) between the resistance roller 120 and the feeding roller 110. Therefore, the urging force (spring force) of the torsion coil spring 140 serves as the transport load (transport resistance) applied to the recording medium P.

Modifications

Modifications of the present exemplary embodiment will now be described.

First Modification

In the above-described exemplary embodiment, the urging unit that urges the resistance roller 120 held by the holder member 150 in a direction opposite to the feeding direction is the torsion coil spring 140. However, the urging unit is not limited to this.

For example, in a feeding device 190 according to a first modification illustrated in FIG. 7, an extension coil spring 141 having an end hooked on a projection 127 may be provided to rotate a resistance roller 121 in the direction of arrow K3. Alternatively, a compression coil or a leaf spring may be used as the urging unit. Alternatively, an elastic member other than a spring, such as rubber, may be used.

Second Modification

In the above-described exemplary embodiment, the transport load (transport resistance) is applied by the arc-shaped resistance member 130 provided on a part of the outer periphery of the roller body 122 that is rotatably held by the holder member 150.

The present invention may also be applied to, for example, a case where a pad-shaped resistance member is used. In a feeding device 200 according to a second modification illustrated in FIGS. 8A and 8B, a plate-shaped resistance member 230 having a flat surface that applies a resistance to the recording medium P is configured to slide along a straight line. The resistance member 230 is urged in the direction of arrow J2 by a compression coil spring 240. As illustrated in FIG. 8B, the movable range of the resistance member 230 in the direction of arrow J1 (feeding direction) is set so that an end portion 234 of the resistance member 230 in the direction of arrow J2 moves past the nip N. When the recording medium P reaches the nip N and is transported, the end portion 234 of the resistance member 230 repeatedly moves past and returns to the nip N (small motion).

Others

The present invention is not limited to the above-described exemplary embodiment.

For example, the structure of the image forming apparatus is not limited to the structure of the above-described exemplary embodiment, and the image forming apparatus may have various structures.

In addition, although the image forming section 14 forms an image on the recording medium P by an electrophotographic method in the above-described exemplary embodiment, the image forming method is not limited to this. An image may be formed on the recording medium P by other methods, such as an inkjet method or a heat transfer method.

Furthermore, although the present invention is applied to the image forming apparatus that forms an image on the recording medium P in the above-described exemplary embodiment, the present invention is not limited to this. The present invention may also be applied to apparatuses other than image forming apparatuses, such as image reading apparatuses, automatic teller machines, and cash registers. The present invention may be applied to any type of feeding device that separates sheets from each other and feeds them one by one.

Furthermore, various embodiments are, of course, possible within the scope of the present invention.

The foregoing description of the exemplary embodiment of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment was chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents. 

What is claimed is:
 1. A sheet feeding device comprising: a feeding member that rotates and feeds a sheet; a resistance member that contacts the feeding member with the sheet interposed therebetween, the resistance member contacting the sheet fed by the feeding member and applying a resistance against the feeding of the sheet; a holding unit that holds the resistance member so that the resistance member is movable to a position where the resistance member does not contact the feeding member; and an urging unit that urges the resistance member held by the holding unit in a direction opposite to a feeding direction of the sheet.
 2. The sheet feeding device according to claim 1, wherein a surface of the resistance member that faces the feeding member is arc shaped in cross section, wherein the resistance member is rotatably held by the holding unit, and wherein the urging unit is a spring that applies a rotational force to the resistance member.
 3. The sheet feeding device according to claim 1, wherein the resistance member includes a flat surface that applies the resistance against the feeding of the sheet.
 4. The sheet feeding device according to claim 2, wherein the holder member includes a rotation fulcrum, and wherein the rotation fulcrum is located so that a contact force between the feeding member and the resistance member increases when the resistance member applies the resistance to the sheet.
 5. The sheet feeding device according to claim 1, wherein the feeding member and the resistance member are not in contact with each other before the feeding member is rotated.
 6. The sheet feeding device according to claim 1, wherein the urging unit is disposed in a central region of the resistance member in a width direction that crosses a movement direction of the resistance member or on each side of the central region in the width direction.
 7. The sheet feeding device according to claim 1, wherein, when a single sheet is nipped between the feeding member and the resistance member, the resistance member is moved against an urging force applied by the urging unit to the position where the resistance member does not contact the feeding member.
 8. The sheet feeding device according to claim 1, wherein, in the case where a single sheet is nipped between the feeding member and the resistance member, when Np is a pressing force with which the resistance member presses the sheet against the feeding member and μ is a coefficient of friction of the resistance member, a force Fp applied to the resistance member in the feeding direction through the single sheet is Fp=Np×μ, and wherein, when Fr is an urging force applied to the resistance member by the urging unit in the direction opposite to the feeding direction of the sheet, Fp>Fr is satisfied.
 9. An image forming apparatus comprising: the sheet feeding device according to claim 1; and an image forming unit which forms an image on the sheet fed by the sheet feeding device. 